In this type of apparatus, it is known that to quench the electric arc which occurs between contacts when a cut-out device is switched off a magnetic field may be used to direct the electric arc towards a chimney which may be shaped like a truncated pyramid ending in a cooling apparatus. Said chimney is provided to length en the electric arc so that its resistance increases until it is quenched.
The efficiency of the cooling apparatus must be high, i.e. the temperature of the gases which emerge therefrom must be as low as possible so as to reduce as far as possible the safety gap which must always be provided in front of the chimney. There are numerous types of cooling apparatus some of which are produced in the form of units with pluralities of circular holes passing right through them which holes allow the plasma to flow through them. These units are made of an insulating plastic, thermoplastic or refractory material. However, due to the fact that the refractory units are drilled, the cylindrical holes are of relatively small cross-section. This results in a high loss of head in the plasma flow. Further, the contact surface area between the gases and the insulating portions which are needed for cooling is necessarily reduced. In other apparatuses, the arc quenching chambers have thick cell partitions fixed on them by screws, said partitions not being compact.
The cooling apparatus in accordance with the present invention remedies these drawbacks. Indeed, in the present invention, the plasma flow is easy although cooling thereof is more effective and the apparatus is as compact as possible.